Flip chip microelectronic assembly is the direct electrical connection of face-down (hence, “flipped”) electronic components onto substrates, circuit boards, another chip, wafer or carriers using conductive solder bumps on the chip bond pads.
In a typical flip chip assembly process, integrated circuits are created on a wafer. Thereafter, pads on a top surface of the integrated circuits are metalized. Next, conductive solder balls (i.e., dots or bumps) are deposited on the pads and the integrated circuits on the wafer are separated or cut from each other. Thereafter, each integrated circuit is “flipped” over and positioned so that the solder balls of the integrated circuit are aligned with mating connectors on the underlying external circuitry. Finally, the solder balls are re-melted and the mounted integrated circuit is “underfilled” using an electrically-insulating adhesive.
During the flip chip assembly process, the solder hardens at or about the same time as vaporized residual flux and its decomposition products deposit on various exposed surfaces. The flux residue should be removed from all critical surfaces prior to further operations on the integrated circuit assembly. A failure to sufficiently remove the flux residue can cause failure of the integrated circuit during long term use due to, for example, stress corrosion during exposure to a temperature and humidity environment.